When it comes to improving the scalability and performance of a web based application with an exponential growth of user numbers, a company has to face several crucial decisions in order to find the most efficient and economically most profitable system architecture. Those decisions also include the introduction of performance increasing methods and technologies. This thesis focuses on increasing the performance of an existing e-learning platform by analyzing and resolving weak-spots in the web server configuration. Subsequently, the initially monolithic system is transformed into a distributed and highly scalable architecture. As a last step, various database solutions have been found, tested, and compared in terms of their performance. Each modification is tested and measured by appropriate metrics. The outcome is a highly scalable system with a significant performance increase.

In the last year, Hadoop YARN has become the defacto standard resource management platform for data-intensive applications, with support for a wide range of data analytics platforms such as Apache Spark, MapReduce V2, MPI, Apache Flink, and Apache Giraph. The ResourceManager fulfills three main functions: it manages the set of active applications (Applications service), it schedules resources (CPU, memory) to applications (the FIFO/Capacity/Fair Scheduler), and it monitors the state of resources in the cluster (ResourceTracker service). Though YARN is more scalable and fault-tolerant than its predecessor, the Job-Tracker in MapReduce, its ResourceManager is still a single point of failure and a performance bottleneck due to its centralized architecture. Single point of failure problem of YARN has been addressed in Hops-YARN that provides multiple ResourceManagers (one active and others on standby), where the ResourceManager’s state is persisted to MYSQL Cluster and can quickly be recovered by a standby ResourceManager in the event of failure of the active ResourceManager. In large YARN clusters, with up to 4000 nodes, the ResourceTracker service handles over one thousand heartbeats per second from the nodes in the cluster (NodeManagers), as such become a scalability bottleneck. Large clusters handle this by reducing the frequency of heartbeats from NodeManagers, but this comes at the cost of reduced interactivity for YARN (slower application startup times), as all communication from the ResourceManager to NodeManagers is sent in response to heartbeat messages. Since Hops-YARN is still using a centralized scheduler for all applications, distributing the ResourceTracker service across multiple nodes will reduce the amount of heartbeat messages that need to be processed per ResourceTracker, thus enabling both larger cluster sizes and lower latency for scheduling containers to applications. In this thesis, we will scale-out the ResourceTracker service, by distributing it over standby ResourceManagers using MySQL NDB Cluster event streaming. As such, the distributed Resource Management for YARN that is designed and developed in this project is a first step towards making the monolithic YARN ResourceManager scalable and more interactive.

In this thesis we will present a study on using lighting to enhance the gameplay of modern board games. Informed by observing board gaming events and getting engaged on forums we learned that besides debating strategies and the game mechanics, another regular discussion is on how to create good environments for games and playing. Based on our findings we frame the design space of light extended board games and propose three types of roles that lighting could play in board games to enhance the gameplay experience: (1) ambiance support for decorative purposes, eg. creating thematic atmosphere, (2) gameplay elements like thematic timers, and (3) game tools such as lighting objects that players can interact with. We designed a light extended board game prototype in order to evaluate several ambiance support and gameplay element role concepts. A Wizard-of-Oz test verified that players experience an enhanced focus using the light extended game. On the other hand, some ambiance support also distracted players. Thematic indications enhance sensory immersion, and randomly triggered elements can make the game more exciting by causing surprise and uncertainty, while reducing player e↵ort. Finally, we conclude this thesis by discussing results and outlining future work.

This thesis aims to develop an audio playback system, which can perform synchronized audio playback on multiple devices. Two different approaches for developing the system has been investigated, one using an already existing off the self product, and the other using an open source framework. The system developed is a proof-of-concept that can perform synchronized playback five devices, connected by Wi-Fi or Ethernet. The system developed can use Bluetooth devices or common media players as the sound source for the system. / Huvuduppgift med detta examensarbete har varit att utveckla ett synkroniserat ljuduppspelningssystem, vilket kan spela upp ljud samtidigt på flera enheter, enheterna är anslutna med antingen med Wi-Fi eller Ethernet. Två olika tillvägagångsätt har undersökts för att utveckla systemet, ett redan färdigt system och ett system baserat på ett ramverk med öppen källkod. Det utvecklade systemet kan utföra synkroniserad uppspelning på fem olika enheter och kan använda Blueetooth enheter och olika mediaspelare som ljudkälla.

As one of the twenty-first century greatest invention, online social network (OSN) is now the central information hubs of million lives, storing and controlling data flow of millions tetra bytes, changing the way information is generating, searching and sharing among people. However, due to the more and more dependence of people to some OSN providers, the data of users are violated and manipulated by providers publicly and aggressively. Many researches recently pinpoint that decentralizing and mobile is inevitable trend of OSN. In this thesis, we explore the neat requirements of DOSN in mobile context and propose a solution satisfying them. We first examine potential weakness and problems in some novel DOSN solutions. Thereafter, the deployment of identity-based cryptography and free cloud storage service is introduced to remedy the existing challenges in existing solutions. In addition, we developed proof-of-concept implementations for the system with a clear API and expandable abilities. The experimental evaluation on the system shows that the approach of using identity-based cryptography for privacy enhancement and identity and trust management is feasible in mobile context. Moreover, the free storage clouds assists content serving well and hence reduces energy and computing resource spent on peer-to-peer mobile networks without adding extra cost.

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Results from the smart-phones' ubiquitous Internet access and diverse multimedia applications, there has been an explosion in mobile data communication, this incredible increase will necessitate continual high energy consumption and leads to more CO2 emissions. It is crucial to develop more energy-efficient systems because of the potential harmful effects to the environment caused by CO2 emissions. It is also significant for the cellular network operators, since the electricity bills are a considerable portion of their Operational Expenditure (OPEX). The power consumption at base stations accounts around 60-80% of the total power consumption in a cellular network [1, 2]. Potential energy savings can be expected by implementing BSs sleeping mode, according to the traffic demands and user activity factors. There are many performance trade-offs in optimizing BSs sleeping modes [3]. One of them is the trade-off between service delay and power consumption of cellular networks. In this thesis, the service delay is considered as a measure of Quality of Service (QoS) user experiences. Based on the conception of cell wilting and dynamic base stations switching, BS sleep switching algorithms are developed while the QoS of User Equipments (UEs) is guaranteed in the meantime. The switching algorithms are decentralized which means no central controller is needed. The BSs can make the switching decisions based on the feedback from UEs and its neighboring BSs. Furthermore, the implementation of the proposed algorithms is also comprehensively described at the protocol level. An urban micro BSs network is built and used as the simulation scenario. Simulations are done with the help of the rudimentary network emulator (RUNE), a network simulator tool developed by Ericsson in MATLAB environment. Simulation results show that up to 62% of power consumption can be saved by implementing the QoS guaranteed BS switching algorithms. Furthermore, comparisons show that the QoS guaranteed BS switching algorithms have higher performance in terms of power consumption savings and QoS to the transitional BS switching algorithms. Many factors inuence the performance of BS switching algorithms. The analysis of the performance is challenging because the required parameters for analysis are dynamically changing during the switching processes. In this thesis, we develop a rough analysis, which gives an insight into some key factors affecting the performance. It shows that high system traffic load results in high power consumption and poor system performance. Either a very small or very large cell radius also leads to high power consumption and poor system performance for different reasons. In addition, choosing different values of the switching threshold affects the system performance in different ways.

In current cellular networks the demand of traffic is rapidly increasing and new techniques need to be developed to accommodate future service requirements. Device-to-Device (D2D) communications is one technique that has been proposed to improve the performance of the system by allowing devices to communicate directly without routing traffic through the base station. This technique has the means to improved performance and support new proximity based services.   Nowadays new applications based on geographical proximity are becoming more and more popular suggesting that D2D communications will have a high de- mand in the near future. Thus the study of the scalability of D2D communications is of paramount importance.   We define the scalability of D2D communications underlay cellular networks as the maximum number of D2D links that can share the cellular resources while assuring QoS to both D2D links and cellular users. In this thesis we study the scalability of D2D communication underlay cellu- lar networks in a multi-cell environment. We propose interference coordination schemes to maximize the number of D2D links while assuring QoS to D2D links and cellular users.   Three interference coordination schemes have been proposed considering dif- ferent levels of available channel state information (CSI). The first scheme is called no CSI centralized (N-CSIC) scheme and it is based on a centralized solution where no CSI is needed. The second is partial CSI distributed (P-CSID) scheme and it is based on a distributed solution where partial CSI is available. The last scheme is named full CSI optimal (F-CSIOp) scheme and it is achieved by formulating an optimization problem considering full CSI to be available.   Extensive mathematical and numerical analysis is conducted to develop and evaluate the proposed schemes. The results show that F-CSIOp scheme offers the best performance followed by the P-CSID and finally N-CSIC, thus a clear relationship is found between complexity and performance.   The P-CSID offers a practical solution for a low complexity interference co- ordination scheme that achieves good scalability and capacity for a wide range of strict QoS requirements. Moreover the results show that further improvement can be achieved if proper selection of the involved parameters is done along with the implementations of closed loop power control (CLPC) schemes.   The N-CSIC scheme provides a good solution for low SINR values of D2D links when the QoS of cellular users is low. Thus it is a good candidate for applications like sensor networks or M2M communications where the SINR requirements are rather low and there are no primary users to impose more interference constraints.   Finally we conclude that good scalability and capacity can be achieved with the proposed low complexity interference coordination schemes for D2D communications and provide interesting topics for future research.

Recommender systems are core components for many companies. These companies constantly improve their functionality aiming to maximize user satisfaction from their products. The only evaluation of the recommender systems usually done by the companies is performed in an online experiment on actual data leaving them without any offline tools to consider and postponing the quality assessment to the time when the algorithm is deployed and used in production. In this work, we describe a software evaluation tool for a selected recommender algorithm applicable for offline cases. We discuss different properties that are important for the assessment of the chosen algorithm, present the user behavior that best reflects expected real life attitude, debate various data sets (available on the Internet and provided by the company) suitable for the offline evaluation. We introduce an extensible software tool for offline assessment that is integrated into test environment created and maintained by Salesforce.com. The tool aims to be exible allowing data sets, user behavior and metrics to be easily switched or used for evaluation of other recommender algorithms. We also describe a set of recommendations on how the selected algorithm could be improved supporting these enhancement suggestions with an evaluation performed using the implemented tool.

Clustered many-core architectures have been successfully exploited in a broad range of applications: from the HPC to the low-power embedded systems. The main goal of this kind of architecture is to provide high computational eciency independently from the workload and the application domain. Depending on the cluster conguration, the number of cores available in these systems can easily grow leading to a huge cost related to threads synchronization. In this optics, this thesis work is focused on the exploration and design of solutions aimed to improve both performance and power consumption of the threads synchronization activity at the cluster level. All the proposed solutions have been develop for an ultra-low power many core platform ( PULP ) targeted to the world of IoT and wearable systems. Busy-waiting synchronization implemented through a Master/Slave mechanism has been replaced with an "event" based synchronization coupled with the clockgating technique. With the introduction of events and clockgating it is possible to put the waiting cores in an idle mode, saving the dynamic energy that otherwise would have been wasted spinning on a local variable. It is also proposed an HW synchronizer, totally supported in the PULP OpenMP library, designed to accelerate threads rendezvous maximizing computational eciency. Synthetic benchmarks have shown an improvement of 4 times comparing the HW synchronizer synchronization cost with the one obtained by the polling solution. On the energy side, application benchmarks, such as Dijkstra algorithm, have shown a dynamic energy reduction up to the 36% with regard to the energy spent during the polling based execution. / Clustered many-core arkitekturer har framgångsrikt utnyttjas på ett brett spektrum av tillämpningar: från HPC till låg effekt inbyggda system. Huvudsyftet med denna typ av arkitektur är att ge hög beräkningseffektivitet oberoende av arbetsbelastningen och ansökan domanen. Beroende på klusterkonfiguration kan antalet core som finns i dessa system lätt växa som leder till en enorm kostnad relaterad till threads synkronisering. I denna optik, är detta examensarbete inriktat på prospektering och utformningen av lösningar som syftar till att förbättra både prestanda och strömförbrukning av threads synkroniserings aktivitet på clusternivå. Alla de föreslagna lösningarna har varit att utveckla en ultra-low power manycore platform (PULP) riktade till en värld av sakernas internet och bärbara system. Busy-wait synkronisering genomförs genom en Master / Slave mekanism har ersatts med en "event" baserad synkronisering tillsammans med clockgating teknik. Med introduktionen av events och clockgating det är möjligt att sätta de väntande core i ett viloläge, vilket sparar den dynamiska energi som annars skulle ha gått till spillo snurra på en lokal variabel. Det föreslås också en HW Synchronizer, helt stod i PULP OpenMP biblioteket, som syftar till att påskynda trådar rendezvous maximera beräkningseffektivitet. Syntetiska benchmarks har visat en förbättring med 4 gånger som jämför HW synkroniseringssynkroniserings kostnad med den som erhålls genom polling lösningen. På energisidan, applikationsriktmärken, såsom Dijkstra algoritm, har visat en dynamisk minskad energiförbrukning upp till 36 % när det gäller energi som går åt under valdbaserade utförande.